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Annotation of OpenXM_contrib/gmp/mpz/tstbit.c, Revision 1.1

1.1     ! maekawa     1: /* mpz_tstbit -- test a specified bit.  Simulate 2's complement representation.
        !             2:
        !             3: Copyright (C) 1997 Free Software Foundation, Inc.
        !             4:
        !             5: This file is part of the GNU MP Library.
        !             6:
        !             7: The GNU MP Library is free software; you can redistribute it and/or modify
        !             8: it under the terms of the GNU Lesser General Public License as published by
        !             9: the Free Software Foundation; either version 2.1 of the License, or (at your
        !            10: option) any later version.
        !            11:
        !            12: The GNU MP Library is distributed in the hope that it will be useful, but
        !            13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
        !            15: License for more details.
        !            16:
        !            17: You should have received a copy of the GNU Lesser General Public License
        !            18: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
        !            19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
        !            20: MA 02111-1307, USA. */
        !            21:
        !            22: #include "gmp.h"
        !            23: #include "gmp-impl.h"
        !            24:
        !            25: int
        !            26: #if __STDC__
        !            27: mpz_tstbit (mpz_srcptr d, unsigned long int bit_index)
        !            28: #else
        !            29: mpz_tstbit (d, bit_index)
        !            30:      mpz_srcptr d;
        !            31:      unsigned long int bit_index;
        !            32: #endif
        !            33: {
        !            34:   mp_size_t dsize = d->_mp_size;
        !            35:   mp_ptr dp = d->_mp_d;
        !            36:   mp_size_t limb_index;
        !            37:
        !            38:   limb_index = bit_index / BITS_PER_MP_LIMB;
        !            39:   if (dsize >= 0)
        !            40:     {
        !            41:       if (limb_index < dsize)
        !            42:        return (dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
        !            43:       else
        !            44:        /* Testing a bit outside of a positive number.  */
        !            45:        return 0;
        !            46:     }
        !            47:   else
        !            48:     {
        !            49:       mp_size_t zero_bound;
        !            50:
        !            51:       dsize = -dsize;
        !            52:
        !            53:       /* Locate the least significant non-zero limb.  */
        !            54:       for (zero_bound = 0; dp[zero_bound] == 0; zero_bound++)
        !            55:        ;
        !            56:
        !            57:       if (limb_index > zero_bound)
        !            58:        {
        !            59:          if (limb_index < dsize)
        !            60:            return (~dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
        !            61:          else
        !            62:            /* Testing a bit outside of a negative number.  */
        !            63:            return 1;
        !            64:        }
        !            65:       else if (limb_index == zero_bound)
        !            66:        return (-dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
        !            67:       else
        !            68:        return 0;
        !            69:     }
        !            70: }